1) Field of the Invention
This invention relates to improvements in needle units used with automated biopsy guns of the type which can be adjusted to allow precise amounts of sample tissue to be collected during a biopsy procedure.
2) Prior Art
The removal of minute tissue samples from humans and animals by introducing a needle into the body and catching the sample within the needle, is a frequently used medical practice today. Such samples are necessary for microscopic examination, organ cultures, etc.
The method most commonly followed for obtaining tissue samples has been to use a needle which is formed of an inner solid rod which has a sampling notch in the distal end thereof, in conjunction with a hollow outer cannula which slides thereover and cuts tissue which has been located in the sampling notch of the inner rod. The inner rod, except for its pointed distal end, is located within the cannula when the device is inserted into the tissue to be sampled. The outer cannula is then held stationary while the inner rod is inserted deeper into the tissue. While in this position, tissue moves into the sampling notch of the inner rod just adjacent the pointed distal tip thereof. The inner rod is then held stationary while the outer cannula is slid thereover. Motion of the outer cannula passing over the sampling notch causes the tissue located therein to be severed from surrounding tissue and thereafter to be trapped in the sampling notch as the cannula completely covers the inner needle distal end. Both the outer cannula and the inner rod with the tissue sample secured therein are then simultaneously removed from the patient. The outer cannula is then slid back away from the distal end of the inner rod to allow removal of the tissue sample from the sampling notch thereof. The tissue sample is then examined.
This general method of tissue sampling has been used for several decades and is exemplified in U.S. Pat. No. 3,477,423. As disclosed therein, the needle movements are made manually. This has certain disadvantages, in that movements may not be made fast enough to insure clean and complete severance of a tissue sample. Further, manual operation of the needle generally involves inaccurate movements, and slight lack of coordination between the needle and the cannula. This often causes unnecessary tissue damage and, in the case of infectious or tumorous tissue, can possibly cause spreading of the diseased tissue throughout a larger tissue area. Also, during manual operation of a needle, the patient may move slightly during the introduction thereof into the tissue and cause the needle to miss its target area. Also, respiratory movements are common for some organs, for example the liver and the kidney, which further may reduce the accuracy of the sampling technique.
An improvement in the above mentioned method of biopsy sampling has been to restrict needle movements by containing the inner rod and outer cannula inside a holder or automated biopsy gun. The biopsy gun restricts needle movement to specific directions and also carries springs and separate piston mechanisms therein which drive the rod and cannula through their sampling motions in a rapid and predictable manner. This technique is exemplified in U.S. Pat. No. 4,699,154. Even though these automated biopsy guns are an improvement over manually actuated needles, they nevertheless have several disadvantages. For example, the length of the needle movement of the conventional automated biopsy guns cannot be adjusted according to the size of the sample desired to be taken. Therefore, unnecessary quantities of tissue may be removed from the tissue sample area causing unnecessary tissue damage and possibly unnecessary spreading of diseased tissue. Further, the forceful introduction of a needle into the tissue area generally causes a certain amount of damage to the tissue in the immediate surroundings of the target area. This is due to the high pressure released from the needle in the injection process.
In my copending U.S. patent application Ser. No. 07/542,324 there is disclosed an improved automatic biopsy gun which allows controlling of the size of a tissue sample taken by the biopsy needle. With the improved biopsy gun, the size of the sample does not exceed the necessary amount of tissue needed for diagnostic purposes. Also, a smaller tissue target area, such as a lesion or tumor or the like can be sampled with a shorter movement of the needle and a smaller and more controlled sample size is taken. This prevents the needle from passing through the target area into unaffected area of the tissue, nor does the needle reach outside of the organ, tumor, lesion, etc. which is being sampled to thereby cause risk of damage to other structures such as adjacent large blood vessels or the like.
With the development of the improved automated biopsy gun, it has been found advantageous to further develop improved needle units to be used with the improved gun. Needle units used with conventional automated biopsy guns comprised an inner needle with a hub attached at one of the ends of the needle. An outer cannula fit over the needle, and another hub was attached to the end of the cannula corresponding to the end of the needle having a hub.
The respective hubs were inserted in mutually respective receiver cavities in the automated biopsy gun. This required a somewhat complicated manual manipulation of the two hubs at a precise spaced apart distance so that the hubs could be inserted int their respective receiver cavities in the automated biopsy guns. In addition, the hubs had to be rotated and oriented in a proper orientation relative to each other for proper placement in the receiver cavities.
Further, with the improved biopsy guns of my copending U.S. application Ser. No. 07/542,324, controlled movement of the piston of the biopsy gun which contacts and therefor drives the hub of the needle is used to control movement of the needle. However, with conventional needle units, the needle itself contributed to uncontrolled movement. This uncontrolled movement occurred primarily when the improved automated biopsy gun was set to achieve a limited movement of the needle, i.e., a movement of the needle which is less than the longest possible movement. In such instances, there was no positive means of preventing further floating movement of the needle especially during the stage of the operation in which the cannula was being moved.